Apparatus for testing dynamoelectric machines



May 5, 1953 B. H. sHoRT APPARATUS FOR TESTING DYNAMOELECTRIC MACHINES Filed April 27, 195o 2 SHEETS- SHEET l l* www W INVENTOR.

Bl H. .SIM/ff BY HIS ATTURNEYS May 5, 1953 B. HQsHoRT APPARATUS FOR TEST-ING DYNAMOELECTRIC MACHINES Filed April 27. .1950

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Arme/wry@ Patented May 5, 1953 APPARATUS FOR TESTING DYNAMO- ELECTRIC MACHINES Brooks H. Short, Anderson, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Belaware Application April 27., 1950, Serial No. 158,441

5 Claims. 1

This application isa continuation in part of my copending application Serial No. 705,003; filed October 23 1946, now abandoned.

This invention relates to apparatus for testing dynamo-electric machines and, more particularly, generators.

An .object of vthe invention `is to provide apparatusincluding a cathode ray tube. on the screen of which there is produced a visible indication of the characteristics of the machine being tested. This object is accomplished by apparatus that senses the acceleration characteristics ofthe tested machine to indicate imperfections if any are present. Since the same iinperfections will affect the operation of a motor or'a generator, the apparatus uses the tested machine as a motor and provides for the indication of imperfections by showing on the tube screen the speed-torque curve of the machine. Faulty construction isV detected by deviation of the speed-torque curve from a speed-torque curve band, which is standard for a good machine made according to the specifications of the machine under test. The apparatus provides two small tachometer generators which are driven by the machine under test. These generators are respectively connected with theY pairs of beam deflecting plates of the cathode ray roscilloscope tube through circuits which sense, respectively,

speed and acceleration. Initially, the machine,

under test, is connected with an operating current source while the armature of the machinev is prevented from rotating. Since full stall current is applied to the machine while the armature is stationary, full stall torque is present. After full stall current is applied 'to the` machine, the armature is released. Since the armature is unloaded except for its own mass and the small mass of rotating parts of the tachometer generators, full torque acts to accelerate this mass. Therefore the acceleration 4of the mass is a function of the .torque available. Since the tube indicates change in speed in relation to speed, it indicates the speed-torque characteristic of the machine.

A further object of the invention is to provide for audibly indicating deviation of the speed- 1 torque curve of the tested machine from a standard curve band.

Further objects and advantages of the present invention wili be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:v

Fig. 1 is a wiring diagram of the apparatus;

2`is a diagram of the screen ofthe cathode ray tube, showing the nature `of the indication which the apparatus produces.

Fig. 3 is a diagram of mechanical connection between the tested machine and tachometer gencraters and controis for the machine.

Fig. 4 is a diagram of means for obtaining audible indication of deviation of the speedtorque curve of the tested machine from a standard curve band.

Referring to Fig. 3, the tested machine, for example, a generator G, has armature brushes connected with terminals a and g, and a field winding F connected with terminals f and y. The generator G may be used with a voltage lregulator (not shown) connected with terminals a and f. For purpose of the test, terminals a and f are directly connected. Terminal g is connected with a current source wire LZ and terminal f is connectible with a current source wire Ll by closing a switch SW2. A solenoid coil SC is connected withthe current source by closing a switch SW2.

Through Va shaft s, generator G drives small tachometer generators i and 50. Shaft s is connected with a toothed disc d against which a dog or pawl p is urged by a spring ps. Pawl p is piv-` oted at p rand is connected by a lever Z with a solenoid armature sa.

To start the test, switch SWS is closed first to subject the machine, operative as a motor, to full stall current and torque. Then switch SW2 is closed to connect coil SC with the current source to cause pawl p to be retracted from disc d so that the machine will turn the generators i0 and 5c at a speed which increases from zero to maximum at a rate which will be shown on the screen of the cathode ray oscilloscope.

Referring to Fig. l, a variable resistance H is connected across terminals of the generator I0, one terminal of which is connected with ground and with the cathode i4 of an ampliiier tube i5 whose grid it is connected with a grid bias battery i3 connected with the adjustable contact l2 of the variable resistance ii. The plate l1 of tube i5 is connected through a resistance i8 with a `plate voltage terminal i9. Plate Il is connected by wire 2l with plate mi of cathode ray tube |00; and the adjacent platey M52 is connected by wire 22 with the movable contact 23 of an adjustable resistance 24. The speedchannel power supply includes transformer 25 whose primary 25 is connected with indicator lamp 2l' and with wires 30 and 32 and whose secondary 23 has its ends connected with plates 29a of rectifier tube .'29 and whose center tap 33 is connected with wire 3c connected with ground and with the resistance 2li. The output of the tube 2t to the plate voltage terminal it is ltered by chokes and 35a and condensers 36. The power supply unit 20 includes a transformer 4B whose'primary si is connected with wires :it and 3i and whose `secondary 42 supplies current for heating the cathodes 29h of the tubes 29.

Tube i5 is a high amplication tube whose change in output voltage is proportional to speed of the machine being tested. In order to effect proper operation of the tube l5, its cathode 4 is -connected with a D. C. source provided by power pack 30 whose input terminals are connected with wires 30 and 3| which are connected with a I volt A. C. source and whose output terminals are connected with a filtering condenser 39. The power pack 38 supplies 6.3 volts D. C. to the cathode i4 of tube E5.

The screen |03 of cathode ray tube |00 on which the cathode ray produces a luminous spot may be considered as having a horizontal axis H and a Vertical axis V (Fig. 2). If the cathode beam is undeected the spot is at S. For example, if under static conditions voltage of plate |1 of tube l5 is '700 volts, the slide 23 is adjusted along the resistance 24 to provide a bucking voltage of 1,100 volts for-example. This causes the spot to move to S1 on axis H.

The terminals of the tachometer generator 59 are connected with a condenser and a sliding contact 52 of an adjustable resistance 53. The junction 54 of the condenser 5| and resistance 53 is grounded and is connected with cathode 58 of an amplier tube 55 whose grid 51 is connected with a grid bias battery 58 connected with a contactor 52 of resistance 53, and whose plate 59 is connected with wire B2 with the grid 6| of an amplifier tube 60 whose plate 53 is connected through resistance 04 with a plate supply terminal S5 of a torque channel power supply unit having a grounded terminal 00. Unit 10 includes a transformer 1| whose primary 12 is connected with wires and 32 and whose secondary 13 is connected at its end with anodes 14 of rectifier tubes 15. ondary 13 is connected with terminal 05. The output of the unit is filtered by chokes 11 and 11a. and capacitors 13. The unit 10 includes a transformer 80 whose primary 8| is connected with wires 39 and 3| and whose secondary 82 supplies current to heat the cathodes 19 of the tubes 15. The cathode 55 of tube 55 is heated by element 33 connected with the secondary 84 of a transformer whose primary 30 is connected with wires 30 and 3|.

The cathode 01 of high amplification tube 50 receives 6.3 volts D. C. from a power pack 38 whose input terminals are connected with wires 30 and 3| and whose output terminals are connected with the cathode 01 and with a filter condenser 39.

Between terminalsi and of the power supply unit 10, there is connected a voltage divider resistance 01 engaged by adjustable contacts 88, 80 and 90. Contact 88 is connected with cathode G1 of tube 00. Contact 89 is connected with a grounded condenser 0| and with a resistance 92 connected with wire 02.

Plate 03 is connected by wire 94 with plate |04 of tube |00, whose adjacent plate |05 is connected by wire 05 with sliding contact 90. Under static conditions, the slider 90 is adjusted so as to cause the spot to move in the direction parallel to the vertical axis V of the screen |03 to a position Sz (Fig. 2), which may be considered the starting position. Distances horizontally from S2 represent speed of the machine under test, and distances vertically above the horizontal line through Sz represent its acceleration or torque. The trace of the cathode ray on the screen |03 having persistent luminosity is a curve (such as L in Fig. 2) which represents the speed-torque characteristic of the machine. The sliding contact 89 is adjusted to give the proper plate supply to the plate 59 of the tube 55. Contact 88 is The center tap 16 of the sec- 4 adjusted to obtain proper bias on the grid 6| of tube 00, this bias being the difference in voltages of wire 52 and contact 80.

The plates |0|, |02 and |04, |05 of tube |00 are located symmetrically with respect to the axis of the tube. The plates |0| and |02 are vertically disposed so that variation in electrostatic field between them will shift the spot horizontally. Plates |04 and |05 are horizontally disposed so that variations in the electrostatic eld between them will shift the spot vertically. The tube |00 has a cathode |00 connected with its cathode heater |01 connected with a secondary |00 of a transformer ||0 whose primary |09 is connected with wires 30 and 3|. Tube |00 has an intensity control element connected with adjustable contact i2, a focusing anode ||3 connected with a sliding contact ||4, a iinal accelerating anode ||5 which is grounded and an intensier anode IIS connected with terminal ||8 of a high voltage power supply unit |20 for the electronic beam. Condenser 22| is connected vbetween wires 22 and 2| and condenser 954 is con-4 the trace of spot S for several seconds after thev curve has been completed. Several hundred volts,

are required by each set of deflecting plates |0|, |02, and |04, |05 to give the maximum usable deection. The unit |20 includes a transformer |2| whose primary |22 is connected with wires 30 and 32 and whose secondary |23 is connected with the anode |24 of a rectier tube |25 whose cathode |26 is connected by wire 9 with terminal ||8. Secondary |23 is also connected with cathode |36 of a rectier tube |35 whose plate |34 is connected with a terminal |28. Transformer secondary |23 is grounded and is connected with a terminal |29. Filter condensers |30 and |3| are connected, respectively, between wire |21 and terminal |29 and between terminal |29 and terminal |20. Cathode heaters |21 and |31 of tubes |25 and |35, respectively, are connected as indicated by arrowheads a, a and b, b with secondaries |42 and |43 of transformers |40 and |4|,y

respectively, whose primaries |44 and |45 are connected with wires 30 and 3|. v

Between the terminals ||1 and |28 of the power supply unit |20, there is connected a voltage divider comprising a resistance |46 engaged by adjustable contact i2, a resistance |41, a resistance |48 engaged by adjustable contact 4 and four resistances |49. cathode |00 with the junction of resistances |40 and |41. The adjustment of contact |2 provides control of intensity and the adjustment of contact 4 provides control of the focusing anode ||3. v

In order to protectthe apparatus against use of the power supply units 20, 10 and |20 before the cathodes of their tubes are heated, a time delay switch unit |50 is provided. Unit |50 includes a relay magnet coil |5| connected with Wires 30 and 3| through a thermostat switch comprising a bimetal blade |52 for engaging a contact |53. The bimetal blade is heated by an element |54 connected with wires 30 and 3|. After a lapse of time suiiicient for the cathodes of the rectifier tubes to become heated, the blade |52 engages the contact |53 to cause energization of the coil |5| which effects the closing of contacts |55 and |55 for connecting wire 32 with wire 3|, a manually operated switch |58 having been previously Wire connects,

closed. The main power source of. 110 volts A. C. is connected with the wires and 3| by the clos# ing o a switch |53 which, when closed, causes an indicator lamp ll) `to burn. When, after closing the switch |58, the relay closes its contacts |55, |56, the lamp 21 burns to indicate that the power supply devices are ready for operation.v

As stated before,- the instrument provides tachometer generators IU and 5|! whose outputs are proportional to the speed of themachine being tested. From these generators there are two channels which influence the operation of vthe tube it in accordance With speed and torque respectively. rlhe speed channel, indicated by heavy lines, includes the generator |75, the amplifier tube I5 and the plates ||i| and |02.` The torque channel, indicated by dash lines,includesgenerator 50, e. differentiating network comprising the adjust able resistance 53 and the condenser 5|, the arm pliiler tubes and E59 and the plates |234 and |05. This diierentiating network causes the feeding of voltage to the amplifier tube' which is di rectly proportional to acceleration of the `machine being tested. This takes place because the voltage impressed on the resistance 53 is proportional to the rate of change of Voltage which is proportional to the acceleration or rate of change' of speed of the machine being tested. In order to obtain this result, the value of resistance 53 must be a small Value so that the normal operation of the condenser 5| will not be appreciably effected by a resistance component.

The machine under test is accelerated rapidly from zero to maximum speed 'to obtain. rapid movement of the spot S on the screen |03 so that there appears thereon a continuous vtrace represented by the line L (Fig. 2) Whichrepresents the speed-acceleration characteristic of the machine being tested. Since the speed-acceleration characteristic oi the machine is an indication of` its torque characteristic', the line l., can be considered a fair indication of the torque-speed characteristic of the machine. Since the same imperfections in the construction of the tested machine will affect the operation of the machine as generator, or as a motor, the trace on the screen can be used to indicate Whether such imperfections are present to such extent that the tested machine Will not pass inspection. For example, let it be assumed that the trace L, shown in Fig. 2, isA the standard of perfection for a good machine lnade according to the specifications of the rhachine under test. of the tested. machine should not deviate :too much from the standard trace L. The limits of allowable deviation are established by placing on the outside of the screen |03, line X for the high limit andline Y for the low limit. Ii' the trace of the tested machine falls betweenlines X and Y, the machine'passes inspection; and if that trace falls outside of line X or line Y, the machine ldoes not pass inspection. To aid the observer, a mask of opaque paper indicated by the shaded area l3 can be placed on the screen |03 between lines X and Y.

Audible as well as Visual indication of failure of a tested machine to pass inspection can be eiected by use of the apparatus shown in Fig. 4. When usine; that apparatus, the ascending portion L of standard trace L is masked also, as indicated by the shaded area below .line Y. The appearance of the trace of the tested. machine outside of the masked area on the screen H33 is detected by the use of a photo-electric cell |lll. When the traceappears at La or at Lb, for example, the cell l'lt To pass inspection, the trace" receives rays-Lr and energizes a relay `,l1 lrwhich connects afcurrent sourceV |12 with an indicatorw lamp |13 and a buzzer or bell |14.

Satisfactory operation .isobtained with the Ich lowing units: Automatic voltage regulator forll v. 60 cycle iA.Y C. input to wires 30 and 3| may beca Condensers Stand 18 Resistances 24 and 81 2 Inicrofarads.v .50 megohm,

watts. Power supply unit Iza'.

Transformer |2| Thordarson T45158. Tubes |25 and y|35 2 X `2. Condenserslll and |3| 1 microfaiad. 3090 volts.4 Resistance |46 1.5 4rnegohxns. Resistance |41 1 megohm. Resistance Ult 5 megohms; Resistance IM 2 megohms. Transformers I4E|,.|4|, Thordarson T- 19F82, cutputztl volts.

Cathode ray tube Du Mont20AP2.

Condenser 22| .5 microfarad. Condenser 954 .3 microfarad.

Speed channel:

D. C. tachometer -genl I crater` |0 Es t er1 i ne kvAngus ModelC.' Resistance Ml megohm.. .Battery v|3 `'7.5volts. Tube l5 #811..A Resistance I8 .375 rnesohrn.'

Acceleration (torque) channel: D. C. tachorneter gen- Time delay relay y| 5U is set for 60 secondsdcay.:

While the embodiment of the present invention as hereindisclosed. constitutes a preferred form. it is tc be understood that other forms might be adopted. l

`What is claimed is as follows:

1. Apparatus for testing a dynamo'electricmachine operating.r asa motor and comprising meansV for preventing operationoi the machine whilecurrent` lis being 4applied `.thereto for the purpose of operating the machine as a motor, meansA for rendering the operation preventingv means nonoperative to allow the machine to in..v crease in speed from zero to a maximum value, two generators driven'by the machine and each producing'` voltages Vprolzvortional tov speed, the

rotating parts of the tested machine and the generators providing the mass to be accelerated, a cathode ray oscilloscope tube having pairs of cathode-beam-deiiecting plates, one pair being arranged at right angles to the other pair, and having a screen on which the beam makes a visible trace, means for causing the electrostatic field between one pair of the tube plates to be sensitive to the amount of speed of one of the generators through application of said generator output voltage to said plates, and means for causing the electrostatic eld between the other pair of tube plates to be sensitive to the rate of change of speed of the other generator through application of said other generator output voltage to said other pair of plates whereby the trace on the tube screen is an indication of speed-acceleration characteristics of the machine.

, 2 Apparatus according to claim 1 further characterized by an opaque mask on the tube screen shaped to denne limits of speed-acceleration characteristics within which the machine may pass inspection, a photo-electric cell which is energized when the trace appears beyond the edges of the mask, an indicator and means for causing operation of the indicator when the cell is energized.

3. Apparatus for testing a dynamo-electricmachine operating as a motor, and comprising means for preventing operation of the machine while current is being applied thereto for the purpose of operating the machine as a motor, means for rendering the operation preventing means non-operative to allow the machine to increasein speed from zero to a maximum value, two generators driven by the machine and each producing voltages proportional to speed, the rotating parts of the tested machine and the generators providing the massto be accelerated, a cathode ray voscilloscope -tube having pairs of cathode-beam-delecting plates, one pair being arranged at right angles to the other pair, and having a screen on which the beam makes a visible trace, a speed circuit channel in circuit with one of the generators and one of the pairs of tube plates for causing the electrostatic field between the plates to be sensitive to the amount of speed of that generator through application oi said generator output voltage to one of said pairs of plates, said channel including an amplifier tube connected in circuit with said pair of oscilloscope plates, a voltage divider connected with the terminals of the generator and a circuit comprising a portion of the voltage divider, a grid biasing source and the grid and cathode of the amplier.

tube, a networkin circuit with the other generator and sensitive to the rate of change of speed of saidother generator, and an acceleration circuit channel in circuit 'with said network and the other pair of tube plates whereby the electrostatic eld between the latter is sensitive to the acceleration of said other generator through application of said other generator output voltage to said other pair of plates, whereby the trace on the tube screen indicates the speed-acceleration characteristic of the machine being tested.

4. Apparatus for testing a dynamo-electricmachine operatingas a motor and comprising means for preventing operation of the machine while. current is being applied thereto for the purpose of operating the machine as a motor, means for rendering the operation preventing means non-operative to allow the machine to increase in speed from zero to a maximum value, two generators driven by the machine and each producing voltages proportional to speed, the

rotating parts of the tested machine and the generators providing the mass to be accelerated, a cathode ray oscilloscope tube having pairs of cathode-beam-deiiecting plates, one pair being arranged at right angles to the other pair, and having a screen on which the beam makes a visible trace, a speed circuit channel in circuit with one of the generators and one of the pairs of tube plates for causing the electrostatic field between the plates to be sensitive to the amount of speed of that generator through application of said generator output voltage to said pair of plates, a differentiating network connected with the terminals of said other generator and comfprising a condenser and a resistance in series, an

amplier tube connected with the other pair of oscilloscope plates, and a circuit including said resistance, a grid biasing source and the grid and cathode of the amplier tube, said network providing a voltage to the amplifier tube in direct proportion to the acceleration of the second generator, whereby the trace on the tube screen indicates the speed-acceleration characteristic of the machine being tested.

5. Apparatus for testing a dynamo-electricmachine operating as a motor and comprising means for preventing operation of the machine while current is being applied thereto for the purpose of operating the machine as a motor, means for rendering the operation preventing means non-operative to allow the machine to increase in speed from zero to a maximum value, two generators driven by the machine and each producing voltages proportional to speed, the rotating parts of the tested machine and the generators providing the mass to be accelerated, a cathode ray oscilloscope tube having pairs of cathode-beaindeecting plates, one pair being arranged at right angles to the other pair, and having a screen on which the beam makes a visible trace, a circuit including the output of one of said generators and one pair of said deection plates in which the voltage proportional to the speed of said one generator is applied to one pair of deflection plates of said oscilloscope, said circuit including an amplifier tube or circuit with said pair of oscilloscope plates, a voltage divider connected with the terminals of the generator and a circuit comprising a portion of the voltage divider, a grid biasing source and the grid and cathode of the amplier tube, a diierentiating network connected with the terminals of said other generator and comprising a condenser and a resistance in series, an amplifier tube connected with the other pair of oscilloscope plates, and a circuit including said resistance, a grid biasing source and the grid and cathode of the amplifier tube, said network providing a, voltage to the amplifier tube in direct proportion to the acceleration of the second generator, whereby the trace on the tube screen indicates the speed-acceleration characteristic of the machine being tested.

BROOKS H. SHORT.

References Cited in the le of this patent UNITED STATES'PATENTS Number Name Date 1,096,942 Owens May 19, 1914 1,960,614 Anderson May 29, 1934 2,306,361 Stuart Dec. 22, 1942 2,383,321 Kleber Aug. 21, 1945 2,464,191 Wen Mar. 8, 1949 2,509,743 Olinger May 30, 1950 2,568,406 Packer et al Sept. 18, 1951 

